Transmission lines are utilized, and typically preferred, for many impedance matching applications. For example, RF power amplifier transistors have an extremely low die impedance. As a result, in order for the die to be useful, this low impedance must be transformed to a higher impedance. Thus, a transmission line may be utilized to transform a low die impedance (typically less than 1 ohm) up to a more useful and practical impedance such as 50 ohms.
In an attempt to provide a more practical impedance for an end-user, the device manufacturer may utilize low pass filter matching elements such as inductors and capacitors to increase the inherently low die impedance to a more suitable intermediate impedance. However, wire bonds represent series inductors and because of such low impedances of the device, the height and length of the wire bonds (which affect inductances) must be tightly controlled. In addition, an end user may then utilize various structures and components to raise the intermediate level impedance to his desired impedance such as 50 ohms. Some of the various structures and components that may be used are chip capacitors, air wound inductors and transmission lines. However, these structures and components are typically prone to assembly variation such as solder wicking on the components and positioning tolerances.
Transmission lines are useful in that they avoid many of the above-mentioned problems associated with discrete components. However, a problem with transmission lines is that at low frequencies the line length of transmission lines are impractical, and at low impedances the line width of transmission lines become impractical.
Hence, there exists a need for an improved transmission line technique for providing an impedance transformation from a low impedance up to a more practical impedance that is practical and reliable.